The present invention relates to a method for manufacturing a liquid crystal display. More particularly, present invention relates to an improved method for manufacturing a thin film transistor-liquid crystal display which reduces the number of photolithography processes that must be performed.
A thin film transistor LCD (xe2x80x9cTFT-LCDxe2x80x9d), which uses the thin film transistor as the active device, has various advantages over other LCDs. These advantages include low power consumption, low drive voltage, a thinness, and lightness of weight, among others.
Since the thin film transistor (xe2x80x9cTFTxe2x80x9d) is significantly thinner than a conventional transistor, the process of manufacturing a TFT is complicated, resulting in low productivity and high manufacturing costs. In particular, since a mask is used in every step for manufacturing a TFT, at least seven masks are required. Therefore, various methods for increasing productivity of the TFT and lowering the manufacturing costs have been studied. In particular, a method for reducing the number of the masks used during the manufacturing process has been widely researched.
FIGS. 1 to 5 are sectional views for explaining a conventional method for manufacturing an LCD, as disclosed in U.S. Pat. No. 5,054,887.
In the drawings, reference characters xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d denote a TFT area and a pad area, respectively. Referring to FIG. 1, after forming a first metal film by depositing pure Al on a transparent substrate 2, gate patterns 4 and 4a are formed out of the first metal film by performing a first photolithography on the first metal film. The gate patterns are then used as a gate electrode 4 in the TFT area and as a gate pad 4a in the pad area.
As shown in FIG. 2, after forming by general photolithography a second photoresist pattern (not shown) that covers a portion of the pad area, an anodized film 6 is formed by oxidizing the first metal film using the photoresist pattern as an anti-oxidation film. The anodized film 6 is then formed on the entire surface of the gate electrode 4 formed in the TFT area, and on a portion of the gate pad 4a in the pad area.
Referring to FIG. 3, an insulating film 8 is formed by depositing a layer such as a nitride film over the anodized film 6. A semiconductor film is then formed by subsequently depositing an amorphous silicon film 10 and an amorphous silicon film 12 doped with impurities on the entire surface of the substrate 2 on which the insulating film 8 is formed. A semiconductor film pattern 10 and 12 to be used as an active portion is then formed in the TFT area by performing a third photolithography on the semiconductor film.
As shown in FIG. 4, a fourth photoresist pattern (not shown) is then formed that exposes a portion of the gate pad 4a formed in the pad area by performing a fourth photolithography on the entire surface of the substrate 2 on which the semiconductor film pattern is formed. Then, a contact hole is then formed in the insulating film 8, which contact hole exposes a portion of the gate pad 4a. The contact hole is formed by etching the insulating film 8 using the fourth photoresist pattern as a mask. A source electrode 14a and a drain electrode 14b are then formed in the TFT area by depositing a chromium (xe2x80x9cCrxe2x80x9d) film on the entire surface of the substrate having the contact hole and performing a fifth photolithography on the Cr film. In the pad area, a pad electrode 14c connected to the gate pad 4a through the contact hole is formed. At this time, the impurity doped-amorphous silicon film 12 on the upper portion of the gate electrode 4 formed in the TFT area during the photolithography process is partially etched, thus exposing a portion of the amorphous silicon film 10.
Referring to FIG. 5, a protection film 16 is then formed by depositing an oxide film over the entire surface of the substrate 2 on which the source electrode 14a, the drain electrode 14b and the pad electrode 14c are formed. Then, contact holes are formed that expose a portion of the drain electrode 14b of the TFT area and a portion of the pad electrode 14c of the pad area. The contact holes are formed by performing a sixth photolithography on the protection film 16.
Subsequently, pixel electrodes 18 and 18a are formed by depositing indium tin oxide (xe2x80x9cITOxe2x80x9d), a transparent conductive material, over the entire surface of the substrate, including the contact hole, and performing a seventh photolithography process on the resultant ITO film. As a result of this seventh lithography, the drain electrode 14b and the pixel electrode 18 are connected in the TFT area, and the pad electrode 14c and the pixel electrode 18a are connected in the pad area.
According to the conventional method for manufacturing the LCD, pure aluminum (xe2x80x9cAlxe2x80x9d) is used as the gate electrode material to lower the resistance of a gate line. An anodizing process is therefore required to prevent a hillock caused by the Al. This additional anodizing step complicates the manufacturing process, reduces productivity, and increases manufacturing costs.
It is an object of the present invention to provide an improved method for manufacturing a liquid crystal display in which manufacturing costs are reduced and productivity increased by reducing the number of photolithography processes performed.
It is another object of the present invention to provide a method for manufacturing a liquid crystal display by which it is possible to prevent the deterioration of device characteristics by preventing the generation of an undercut in a gate electrode.
To achieve the above objects, there is provided an improved method for manufacturing a liquid crystal display according to the present invention, comprising the steps of forming a gate electrode and a gate pad by a first photolithography process by sequentially depositing a first metal film and a second metal film over a substrate of a TFT area and a pad area, respectively; forming an insulating film over the entire surface of the substrate on which the gate electrode and the gate pad are formed; forming a semiconductor film pattern over the insulating film of the TFT area using a second photolithography process; forming a source electrode and a drain electrode in the TFT area using a third photolithography process, the source electrode and the drain electrode comprising a third metal film; forming a protection film pattern over the substrate on which the source electrode and the drain electrode are formed using a fourth photolithography process, the protection film pattern exposing a portion of the drain electrode and a portion of the gate pad; and forming a pixel electrode over the substrate on which the protection film pattern is formed using a fifth photolithography process, the pixel electrode being connected to the drain electrode and the gate pad.
The first metal film preferably comprises one of aluminum or an aluminum alloy and the second metal film comprises a refractory metal. More specifically, the second metal film preferably comprises a metal selected from the group consisting of Cr, Ta, Mo, and Ti.
The step of forming the gate electrode includes the steps of forming the first metal film and the second metal film over a substrate in the described order; forming a photoresist pattern over a portion of the second metal film; etching the second metal film using the photoresist pattern as a mask; reflowing the photoresist pattern; etching the first metal film using the reflowed photoresist pattern as a mask; and removing the reflowed photoresist pattern. The step of reflowing the photoresist pattern may be performed in multiple steps.
The step of forming the gate electrode preferably includes the steps of forming the first metal film and the second metal film on the substrate in the described order; forming a photoresist pattern on a portion of the second metal film; etching the second metal film by etching using the photoresist pattern as a mask; and etching the first metal film. The etching of the second metal film may be either a wet or dry etch and a step of baking the photoresist pattern may be included after the step of etching the second metal film.
The step of forming the gate electrode preferably includes the steps of forming the first metal film and the second metal film on a substrate; forming a photoresist pattern on a portion of the second metal film; etching the second metal film using the photoresist pattern as a mask; etching the first metal film using the patterned second metal film; and re-etching the patterned second metal film. A step of baking the photoresist pattern may be included prior to the step of etching the first metal film after the step of etching the second metal film.
According to the present invention, it is possible to prevent a battery effect and a hillock caused by directly contact of Al to the ITO by forming the gate electrode in a double structure of Al or an Al alloy and a refractory metal film. Also, it is possible to omit the anodizing process and to simultaneously etch the insulating layer and the protection film due to a capping film, thus reducing the number of the photolithography processes. Also, since it is possible to form the first metal film larger than or identical to the second metal film, an undercut is not generated in the gate electrode. Therefore, it is possible to prevent the deterioration of insulation characteristics due to poor step coverage during deposition of the insulating film after forming the gate electrode.